how do I add values prefixed with a letter

Hi guys this is prob really easy easy to do but I'm stumped.

I have a column which I simply enter overtime hours into and it is totalled up at the bottom, easy. I now have to on given days enter TOIL taken (time of in lieu) I'm thinking to distinguish from overtime hours entering it as T2 for 2 hrs TOIL etc. Is there a way that this entry can be added up recognising the T infront of the number. So far I've tried this =COUNTIF(C6:AG6,"t*") which allows me to enter T and a value but it only counts the number of times I enter a value of T3 etc and not the total. Hope that is as clear as mud. If I'm going down the wrong avenue then please point in the right direction.

Thanks in advance